This week in animal research: w/e 29 August

Artificially activating circuits in the mouse brain can change bad memories into good ones. Male mice weregiven bad memories of a particular location consisting of small electric shocks. The neurons storing this‘place’ memory were then re-activated in a different emotional context – the presence of a female – whichmodified the memory association from bad to good. The findings are unlikely to be applied to the treatment ofhuman traumatic memories, but the work has been hailed by other researchers as an important step inunderstanding how these memories are formed and influenced. "Nobody's going to be queuing up to havelight guides inserted into their brain and have blue light shone down into it,” said Prof Richard Morris, whowas not involved with the study, “but these results will help us understand the proportion fo cells that areinvolved when you have to change a memory.”

Some fish can adapt to living out of water including developing the way that they walk, giving scientists anidea of how the prehistoric fish ancestors of all terrestrial vertebrates first left the oceans. Polypterus fish fromSouth Africa have lungs, are capable of breathing air, and can ‘walk’ on land using their fins betweenunconnected patches of water. The researcher took juvenile fish and raised them on land, and found that aftereight months these fish had developed a more sophisticated style of walking than aquatically raised controls.Their bone structure and musculature also changed to be more suited to walking.

The natural embryonic development of the spinal cord has been successfully mimicked in vitro using bothmouse and human cells. This study raises the hope that complex neuromuscular conditions could one day betreated by transplanted complex, lab grown human tissue. As well as paving the way for future treatments,this breakthrough will enable scientists to study the development of diseases like motor neurone disease bytaking cells from patients and seeing how their development differs from healthy cells.

Studies in mice have shown that clostridia bacteria in the gut can help to prevent allergies, and can even beused to treat peanut allergy. Mice reared in an entirely sterile environment, with no gut bacteria, experienceda strong immune response to peanut. Researchers at the University of Chicago introduced different bacteriainto the guts of these mice, and found that only Clostridia could prevent the allergic reaction. They believethat the bacteria prevent the peanut allergens from entering the bloodstream where they cause the allergicreaction. Prof Colin Hill from University College Cork commented that “While we have to be careful not toextrapolate too far from a single study, and we also have to bear in mind that germ-free mice are a long wayfrom humans, it is a very exciting paper and puts this theory on a much sounder scientific basis.”

A whole functional organ has been grown from scratch inside a mouse for the first time. Scientists from theUniversity of Edinburgh took cell from a mouse embryo and genetically ‘reprogrammed’ to become a type ofcell found in the thymus, a critical organ in the immune system. Once placed inside the mice the cellsdeveloped into a functioning thymus. Translating this finding to humans will not be straightforward due to anumber of issues, but Prof Clare Blackburn, part of the research team, said it was "tremendously exciting"when the team realised what they had achieved. "This is a very exciting advance and it's also very tantalisingin terms of the wider field of regenerative medicine."

Toxoplasma gondii, otherwise known as the terrifying mind control cat parasite, appears to control thebehaviour of its hosts by making subtle changes to their DNA. Rats are known to be less fearful of cats wheninfected with the parasite, a change that appears to be linked to region of DNA in the amygdala of the brainthat is 'unsilenced' by the parasite causing the release of excess neurotransmitter. When this DNA was re-slienced, researchers found that the rats regained their fear of cats.